The present invention relates to a tube with suction slots for a unit for condensing a bundle of textile fibres drafted in a spinning machine.
The field of application of the present invention is that of spinning machines having a plurality of adjacent spinning stations in each of which there is a drafting unit associated with a condensing unit for treating a bundle of textile fibres, or roving, to be transformed into a twisted yarn.
For a better understanding of the prior art and of the problems inherent therein, a conventional condensing unit will be described first of all with reference to FIGS. 1 and 2 of the appended drawings.
In FIG. 1, a bundle of textile fibres or roving 1 is supplied to a drafting unit, generally indicated 2, comprising three pairs of rollers 3 and 4, 5 and 6, 7 and 8, which pull the roving along at increasing linear velocities in order to thin it gradually. The roving output from the drafting unit 2 then goes to a condensing unit 10 located downstream of the drafting unit, before being sent for twisting.
The condensing unit 10 comprises a lower fixed tube 11 of circular cross-section, connected to a suction source (not shown), by means of a manifold 12. As shown in FIG. 2, the tube 11, which is common to several spinning stations located side by side, has, in each station, a narrow suction slot 15 arranged on the path of and in the direction of movement of the roving.
A plurality of freely rotatable cylindrical sleeves 16 are mounted along the tube 11, there being one sleeve in the region of each spinning station and each sleeve having a central perforated portion 17 which extends around the entire circumference of the sleeve and covers the corresponding slot 15 with a large margin. Each sleeve 16 is driven so as to move around the tube 11 by a pressure roller 18 of elastomeric material which presses the roving against the perforated portion 17 of the filtering sleeve 16. The pressure roller 18 is rotated by the last pressure roller 7 of the drafting unit 2, by means of a belt transmission 19.
As shown in FIG. 2, the outer surface of the fixed tube 11 is machined to form cylindrical recesses 13 which house locating rings 9 that perform the dual functions of:
keeping the sleeves 16 correctly positioned axially along the tube so that the central perforated portions 17 of the sleeves are located over on the respective suction slots 15, and
limiting the area of the sliding contact surface between the sleeve 16 and the tube 11 to the narrow region of the recesses 13.
An example of this prior art is described in EP-1106719-A, which is incorporated herein by reference.
An object of the present invention is to provide a condensing unit of simple and inexpensive construction which, in particular, reduces the costs connected with the machining of the tube to render it suitable for housing the above-mentioned locating rings.
A further object of the invention is to provide a condensing unit which does not have the above-mentioned conventional locating rings.
These and other objects and advantages which will be understood further from the following description are achieved, according to the present invention, by a novel condensing unit.